🛰️ background_locator

A Flutter plugin for updating location even if the app is killed

How it work 🙋

• The plugins register an Isolate as START_STICKY so it can't be killed by Android

• It will execute a static callback function in your dart code where you execute everything except any UI operation (static because it can't be accessed otherwise 😉)

• To change any UI element, you need to listen to the Isolate port that the callback function will send to

More info on Isolate : Isolates and Event Loops - Flutter in Focus

📝 Example :

At every callback, append the location in a file, on app start, recover the position list from this file and put it on the map as a polyline

Install 📥:

1. Depend on it

Add this to your package's pubspec.yaml file:

dependencies:
  background_locator: ^1.1.2+1

You can remove ^1.1.2+1 to always get the latest version

2. Install it

You can install packages from the command line:

with Flutter:

$ flutter pub get

Alternatively, your editor might support flutter pub get. Check the docs for your editor to learn more.

3. Import it

Now in your Dart code, you can use:

import 'package:background_locator/background_locator.dart';

Setup ⚙️:

🤖 Android

1. Make sure to have the following permissions inside your AndroidManifest.xml:

    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <uses-permission android:name="android.permission.ACCESS_BACKGROUND_LOCATION" />
    <uses-permission android:name="android.permission.WAKE_LOCK"/>
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>

• ACCESS_FINE_LOCATION to have the GPS 🛰️

Note: you can set ACCESS_COARSE_LOCATION but you will have to modify the accuracy below LocationAccuracy.LOW

• ACCESS_BACKGROUND_LOCATION To get update in background ✅
• WAKE_LOCK to not sleep while getting the GPS 😴
• FOREGROUND_SERVICE To let the plugins operate as a service ⚙️

2. Add also the following lines to your AndroidManifest.xml to give the plugins's services their liberties:

    <!-- If you want to get update when the app is in background
        but not when it is killed you can add android:stopWithTask="true"
        to these tree services -->
        <receiver android:name="rekab.app.background_locator.LocatorBroadcastReceiver"
            android:enabled="true"
            android:exported="true"/>
        <service android:name="rekab.app.background_locator.LocatorService"
            android:permission="android.permission.BIND_JOB_SERVICE"
            android:exported="true"/>
        <service android:name="rekab.app.background_locator.IsolateHolderService"
            android:permission="android.permission.FOREGROUND_SERVICE"
            android:exported="true"/>

        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />

3. To work with other plugins, even when the application is killed (using path_provider for example), create a new file inside android/app/src/main/kotlin/com/example/YourFlutterApp/ named LocationService.kt and fill it with :

package rekab.app.background_locator_example

import io.flutter.app.FlutterApplication
import io.flutter.plugin.common.PluginRegistry
import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback
import io.flutter.plugins.pathprovider.PathProviderPlugin
import io.flutter.view.FlutterMain
import rekab.app.background_locator.LocatorService

class LocationService : FlutterApplication(), PluginRegistrantCallback {
    override fun onCreate() {
        super.onCreate()
        LocatorService.setPluginRegistrant(this)
        FlutterMain.startInitialization(this)
    }
    
    override fun registerWith(registry: PluginRegistry?) {
        if (!registry!!.hasPlugin("io.flutter.plugins.pathprovider")) {
            PathProviderPlugin.registerWith(registry!!.registrarFor("io.flutter.plugins.pathprovider"))
        }
    }
}

4. Again, inside your AndroidManifest.xml change android:name from io.flutter.app.FlutterApplication to rekab.app.background_locator_example.LocationService to register the step 3:

<application
        android:name="rekab.app.background_locator_example.LocationService"

Great ! 👍 Its now your turn, inside your dart file create a callback function that the plugin will call in background

📝 Example :

import 'package:path_provider/path_provider.dart';

static void callback(LocationDto locationDto) async {
  print('location in dart: ${locationDto.toString()}');
  final SendPort send = IsolateNameServer.lookupPortByName(_isolateName);
  send?.send(locationDto);
  //the '?' check if send is null before executing it

  final file = await _getTempLogFile();
  await file.writeAsString(locationDto.toString(), mode: FileMode.append);
}

🍏 iOS

1. Add the following lines to AppDelegate class:

import background_locator

func registerPlugins(registry: FlutterPluginRegistry) -> () {
    GeneratedPluginRegistrant.register(with: registry)
}

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    BackgroundLocatorPlugin.setPluginRegistrantCallback(registerPlugins)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

2. In app settings enable Background Modes and check Location Updates.

3. In Info.plist add Key for using location service:

NSLocationAlwaysAndWhenInUseUsageDescription
NSLocationWhenInUseUsageDescription

How to use it 👨‍💻:

See the best practices here : Example app

1. Initialize plugin:

static const String _isolateName = "LocatorIsolate";
ReceivePort port = ReceivePort();

@override
  void initState() {
    super.initState();
    
    //override the previous port by this one, we can't
    //re-use the previous port
    if (IsolateNameServer.lookupPortByName(_isolateName) != null) {
        IsolateNameServer.removePortNameMapping(_isolateName);
    }
    
    IsolateNameServer.registerPortWithName(port.sendPort, _isolateName);
    port.listen((dynamic data) {
      // do something with data
    });
    initPlatformState();
  }
  
Future<void> initPlatformState() async {
    await BackgroundLocator.initialize();
}

2. Create the callback function, Also the notification callback if you need it:

static void callback(LocationDto locationDto) async {
    final SendPort send = IsolateNameServer.lookupPortByName(_isolateName);
    send?.send(locationDto);
  }

//Optional
static void notificationCallback() {
    print('User clicked on the notification');
  }

3. Start the location service :

Before starting the plugin make sure to have the necessary permissions

//Somewhere in your code
startLocationService();

void startLocationService(){
    BackgroundLocator.registerLocationUpdate(
        callback,
        //optional
        androidNotificationCallback: notificationCallback,
        settings: LocationSettings(
            //Scroll down to see the different options
            notificationTitle: "Start Location Tracking example",
            notificationMsg: "Track location in background exapmle",
            wakeLockTime: 20,
            autoStop: false,
            interval: 1
        ),
    );
}

3. Unregister the service when you are done:

@override
void dispose() {
    IsolateNameServer.removePortNameMapping(_isolateName);
    BackgroundLocator.unRegisterLocationUpdate();
    super.dispose();
}

LocationSettings options ⚙️:

accuracy: Accuracy of location, default : LocationAccuracy.NAVIGATION

• LocationAccuracy.NAVIGATION
• LocationAccuracy.HIGH
• LocationAccuracy.BALANCED
• LocationAccuracy.POWERSAVE
• LocationAccuracy.LOW

interval: Interval of request the service make in second only for Android, default : 5

distanceFilter: Distance in meter to trigger the callback, Default : 0

notificationTitle: Title of the notification only for Android, default : 'Start Location Tracking'

notificationMsg: Message of the notification, only for Android default : 'Track location in background'

notificationIcon: Image of the notification, only for Android, the icon should be in 'mipmap' directory. Default : App icon

wakeLockTime: Timeout in minutes for the service, only for Android, default : 60

autoStop: If true the service will stop as soon as app goes to background